Well done on everything inc. weaning off the shield.
'drunken milk look' sounds perfect!
15-20 minutes is almost certainly sufficient if she's pulling off herself with that look!
As for the waking up to burp - some breastfed babies need very little burping or even none. (another good reason to stick with boob)
I wouldn't wake her up if she's sleeping contently and has fed well. If she's turning away from second breast she sounds done.
As to whether she's getting enough - check out wet nappies (around 6 in 24 hours), wet eyes, at least 3 poos a day (but that can change around 6 weeks and it can really slow down which is fine). If they're happy with weight gain though I think you can assume she is.
It all sounds great!